On Nov 10, 2013, at 10:12 PM, Stan Hoeppner [off-list ref] wrote:

USB is not a storage protocol.  USB devices often disconnect/reconnect
for no apparent reason.  We see this frequently with the little vendor
USB disk drives (Seagate/WD) and also generic disk enclosures.  USB is
not a proper protocol for md/RAID storage.  You may have continual
problems with this setup.

If the laptop has an eSATA port use eSATA.  If not, drop in an eSATA
PCMCIA card.  This should be much more reliable than USB for this
application.

Actually, it's a good piece of advice. Now all I need is to figure out if I I can do this with the hardware I've got.

However, I feel compelled to say that my USB drives (I have had several… 4 to be precise, now 5) have been incredibly reliable throughout all these years. No connection problems whatsoever, no flakiness/flapping of any kind. Very solid and reliable as for a home, midrange 7 years old laptop and three 7 years old drives. I've been using them for all sorts of things, from backups to torrents and storing virtual machine disk images, etc. Very reliable. The only concern I have is that performance sometimes may not be enough, but by and large it is not a problem for me and so I get by just fine.

Installing an eSATA PCMCIA card is actually a great idea, and I almost falmpaced when I realized I could've probably resolved performance issues long time ago and the solution was in front of me all this time, but then again the problem was from a pressing character and so I have been really content most of the time with what I have.

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Also, I see little/no value in running a scheduled mdadm check on a
RAID1 array.  Any problems with RAID1 will be due to one of the disks
beginning to fail in some mode, usually requiring sector relocation.
Most drives do this automatically until they run out of spare sectors,
at which point md will throw write errors.  Monitoring SMART data and/or
running SMART self analysis on a schedule is much more effective here,
as you will become aware of a problem sooner, and have the opportunity
to correct it before it shows up in md.

Bare with me, I know very little about how RAID works so I can sometimes make totally absurd statements. That being said, I intend to monitor SMART values and I'm wondering now why does it make sense to run check on other types of RAID? I assume 5/6/10 mostly?

I'm also wondering if it is advised to run check with filesystem mounted and in use, or unmounted?

Instead of using a connection method known to cause problems with
storage, and then attempting to mitigate such damage with array/fs
checks after the fact, why not simply avoid the problem in the first
place?  Use eSATA, or build/buy a little NFS/Samba NAS filer.

As I said in my particular configuration it is a pretty solid connection. No experience with NAS filers here, but I'm definitely looking this option up as well (already googled it up and reading a description).

What about filesystem state? Does it matter if a filesystem is mounted when check is run?

Ivan

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